Many electrical components generate heat during periods of operation. If this heat is not removed from the electrical component in an efficient manner, it will build up. Malfunction or permanent damage to the electrical components may then result. Therefore, thermal management techniques are often implemented within electrical circuits and systems to facilitate heat removal during periods of operation.
Thermal management techniques often involve the use of some form of heat sink to conduct heat away from high temperature areas in an electrical system. A heat sink is a structure formed from a high thermal conductivity material (e.g., typically a metal) that is mechanically coupled to an electrical component to aid in heat removal. In a relatively simple form, a heat sink can include a piece of metal (e.g., aluminum or copper) that is in contact with the electrical circuit during operation. Heat from the electrical circuit flows into the heat sink through the mechanical interface between the units.
In a typical electrical component, a heat sink is mechanically coupled to the heat producing component during operation by positioning a flat surface of the heat sink against a flat surface of the electrical component and holding the heat sink in place using some form of adhesive or fastener. As can be appreciated, the surface of the heat sink and the surface of the component will rarely be perfectly planar or smooth, so air gaps will generally exist between the surfaces. As is generally well known, the existence of air gaps between two opposing surfaces reduces the ability to transfer heat through the interface between the surfaces. Thus, these air gaps reduce the effectiveness and value of the heat sink as a thermal management device. To address this problem, polymeric compositions have been developed for placement between the heat transfer surfaces to decrease the thermal resistance there between. The bulk thermal conductivity of current thermal interface materials is largely limited by the low thermal conductivity of polymer matrices (˜0.2 W/m-K for polymers typically found in thermal interface materials or TIMs). By some estimates (“Thermally Conductive Polymer Compositions,” D. M. Bigg., Polymer Composites, June 1986, Vol. 7, No.3), the maximum bulk thermal conductivity attainable by electrically insulating polymer composites is only 20–30 times that of the base polymer matrices. This number changes little regardless of the filler type, once the thermal conductivity of the filler exceeds 100 times that of the base polymer matrix. Consequently, the thermal conductivity of polymeric materials is low compared to the thermal conductivity of the heat sink, resulting in an inefficient transfer of heat from the heat producing component to the heat sink. In addition, effective heat transfer capability is further reduced by interfacial imperfections due to 1) micro or nanovoids, and 2) a filler-depleted layer caused by filler settlement or the inability of micro-sized filler to penetrate into surface irregularities that are smaller than the filler size.
A need therefore exists for improved compositions to effectively transfer heat between a heat sink and a heat producing component.